A LED scribing process is one of examples of a laser processing process using a pulse laser. LED (Light Emitting Diode) is one of light emitting elements using a semiconductor which receives current and emits light. Recently, as a semiconductor technology advances, production of LED elements of high quality has become available. By way of example, it has been generalized that a III-IV group nitride layer is formed on a sapphire substrate by a metal organic chemical vapor deposition (MOCVD) method to produce a blue LED of high luminance.
However, in case where a sapphire substrate is processed with a conventional laser processing apparatus, there has been a problem as follows.
In case where a sapphire substrate is scribed or cut with a conventional laser processing apparatus, the sapphire substrate may have a poor cutting surface and luminance may be decreased, which has been a major problem as LED elements of high luminance are required in recent years. A mechanism of decreasing luminance by a cutting process has not exactly been known, but it has been deemed that an amorphous region formed around a cut region absorb lights, which causes a decrease in luminance.
Further, in case where the sapphire substrate is processed with a conventional laser processing apparatus, fine dust may be generated when the sapphire substrate is cut, which may have a bad influence on element characteristics. In the process using the conventional laser processing apparatus, a cut region of a relatively large area may be formed, and, thus, there has been a limit in integrating a multiple number of functional devices on a single wafer with high density.
Furthermore, by way of example, a stacked portion formed of a nitride layer is formed on a sapphire substrate, and if a laser beam is irradiated passing through the nitride layer, heat may be generated between the substrate and the nitride layer or defects such as cracks or peeling may be generated therebetween.